In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art.
Polymers have long been given antimicrobial properties, usually by the purely physical mixing of an antimicrobial active ingredient into a corresponding material matrix. Thus for example in WO 98/48766 a tooth-coating material for the prevention of caries is described which contains triclosan (2,4,4′-trichloro-2′-hydroxydiphenylether) as antimicrobial active ingredient. Materials for dental use such as prosthetic plastics and fixing cements which contain antimicrobial phenolic substances such as triclosan are also described in US 2003/0220416.
DE 198 13 686 discloses a gutta-percha-based root-canal filling material which releases chlorhexidine as antimicrobial active ingredient.
US 2005/0080158 describes a UV-curing wood-coating material which contains triclosan, WO 2004/098658 proposes among other things the use of quaternary ammonium salts as antimicrobial active ingredients for polymeric coating materials for the building industry.
The purely physical mixing of antimicrobial active ingredients into a material is encumbered by several problems. In order to achieve its antimicrobial effect, the agent must be released over the period of action of the material. As a rule, the release rates are such that the agent is initially released in a very high concentration and thereafter the antimicrobial effect is largely lost. Another disadvantage is that at high agent concentrations toxic side-effects can occur, which is undesirable in particular in medical applications such as, e.g., contact lenses or dental materials. In addition, with continuous or increased release of agent there is a risk of resistance forming. For this reason, in particular for such applications, there has been a switch to making the agent polymerizable in order to immobilize it during the curing of the material by homopolymerization or copolymerization with another polymerizable monomer in the forming polymer.
U.S. Pat. No. 5,536,861 and U.S. Pat. No. 5,358,688 disclose organosilicone monomers which contain a quaternary ammonium group as antimicrobial group for use in contact lenses.
EP 0 663 409 discloses monomers which contain quaternary phosphonium groups as active group for use in contact lenses.
In EP 0 537 774 polymerizable active-ingredient monomers which contain a quaternary ammonium group are described. (Meth)acryl functionalities are used as polymerizable group, an alkylene spacer with 2 to 18 C atoms being located between the polymerizable group and the active group.
In EP 0 705 590 and WO 01/90251 special compositions for dental use which contain an antimicrobial, polymerizable monomer according to EP 0 537 774 are described.
A disadvantage when using polymerizable active ingredient monomers is that in most cases only the monomer has an antimicrobial effect, which is lost after the polymerization. Often, only residual monomer present is responsible for the antimicrobial effect of the polymers, with the result that after the elution of the non-polymerized antimicrobial monomers the antimicrobial effect of the materials diminishes. The antimicrobial long-term effect is thus significantly reduced, as a result of which, e.g., drugs or medicinal products at least partly lose their clinical capability.
DE 196 46 965 A1 discloses polymers with antimicrobial properties which consist of vinylically polymerizable monomers and of monomers in which at least one long-chained alkyl radical is bonded to a quaternary ammonium group which for its part is bonded via a hydrophilic spacer to a vinyl function. The polymers are to be suitable for the preparation of paints such as, e.g., marine paints and mouldings such as, e.g., bathroom and kitchen surfaces.
WO 00/69926 discloses a process for the preparation of inherently antimicrobial polymers by polymerization of monomers which have at least one quaternary amino function. The monomers can have a hydrocarbon radical with up to 50 carbon atoms and have a molecular mass of less than 900. The polymers are to be suitable for the preparation of varnishes, protective paints and coatings, e.g., for ship hulls, toiletries, contact lenses, membranes and implants.